Are there health concerns from breastfeeding or letting someone drink my milk?

It's perfectly fine to try another person's breast milk if you know their health history. Breast milk is a body fluid and therefore it's possible to transmit pathogens.
The next biggest concern is Mastitis (warning:NSFW) which can be lessened with Lecithin and a proper latch technique (warning:NSFW). The Piercings and Lactation page (warning:NSFW) addresses this concern as well.

Depending on which site you're on, you might be able to use our memes (warning:NSFW) or make your own. Additionally, the site logo is free to use to upload to your profile; pin button and flyer templates are now available.